The present invention relates to a method and system for cleaning semiconductor substrates or treating semiconductor substrates ready for etching. More particularly, the present invention relates to a cleaning/etching method and a cleaning/etching apparatus for semiconductor substrates moving along the production line for cleaning or etching.
Production of semiconductors involves very important processes for wet-cleaning and etching semiconductor substrates or wafers. Higher density devices than before need further high-performance cleaning and etching. The wet-cleaning and etching processes in the production of semiconductors nowadays employ a variety of chemical solutions for specific individual objects. They include ammonia water, hydrochloric acid, hydrogen peroxide water, hydrofluoric acid, sulfuric acid, phosphoric acid, nitric acid, etc.
For example, removal of particles is usually accomplished by APM cleaning (with a mixed liquid of ammonia, hydrogen peroxide water, and water) and removal of metal is usually accomplished by SPM cleaning (with a mixed liquid of sulfuric acid and hydrogen peroxide water) or HPM cleaning (with a mixed liquid of hydrochloric acid, hydrogen peroxide water, and water).
Moreover, wet etching of silicon oxide film usually employs a mixed liquid of hydrofluoric acid and water or a mixed liquid of ammonium fluoride, hydrofluoric acid, and water (buffered hydrofluoric acid), and wet etching of silicon nitride film usually employs hot phosphoric acid. Thus, a variety of chemical solutions are indispensable for cleaning and wet etching.
In the meantime, a recent development is cleaning with ozone water for removal of organic contaminants. A conventional cleaning system with ozone water is schematically shown in FIG. 9. A cleaning apparatus 1 permits the ozone concentration to be set as desired. The set value is sent to the ozone gas generating unit 2 through a signal circuit 4. An ozone gas generating unit 2 adjusts the discharge voltage according to the signals received, so that it generates as much ozone gas as necessary. The ozone gas is dissolved in pure water through membranes in the ozone dissolving unit 3. The resulting ozone water is supplied to the cleaning apparatus 1.
However, in the conventional cleaning system, setting the ozone concentration necessary for the cleaning apparatus 1 by adjusting the discharge voltage in the ozone gas generating unit 2 leads to the disadvantage that it takes time for the discharge voltage to become stable, it takes time for ozone gas of a prescribed amount to enter the ozone dissolving unit 3 (because of some distance between the ozone gas generating unit 2 and the ozone gas dissolving unit 3), and it takes time for ozone water of a desirable concentration to enter the cleaning apparatus 1.
Incidentally, the prior art technology of substrate treatment with an ozone-containing chemical solution or pure water is disclosed in Japanese Patent Laid-open No. Sho 60-239028 and U.S. Pat. No. 5,567,244. However, difficulties are presented in controlling the ozone concentration rapidly and freely.
It is an object of the present invention to provide a method and system of treating semiconductor substrates, said system and method being used in the wet cleaning and etching of semiconductor substrates so as to improve yields while preventing surface roughening. According to the present invention, the method and system for treatment employ ozone or ozone-containing active oxygen as the treating medium and are capable of freely controlling the concentration of ozone or ozone-containing active oxygen, thereby improving throughputs.
According to one aspect of the present invention, in a method of treating semiconductor substrates, ozone is generated and dissolved in a chemical solution or pure water for treatment of semiconductor substrates. The chemical solution or pure water in which the ozone has been dissolved is irradiated with ultraviolet light, and thereby the concentration of the ozone in the chemical solution or pure water is controlled. Then, semiconductor substrates are treated with the chemical solution or pure water containing the ozone in controlled concentrations.
According to another aspect of the present invention, in a method of treating semiconductor substrates, oxygen is generated and dissolved in a chemical solution or pure water for treatment of semiconductor substrates. The chemical solution or pure water in which the oxygen has been dissolved is irradiated with ultraviolet light, and thereby active oxygen is generated and the concentration thereof is controlled. Then, semiconductor substrates are treated with the chemical solution or pure water containing the active oxygen in controlled concentrations.
In the methods of treating semiconductor substrates, phosphoric acid is preferably employed as the chemical solution. Alternatively, hydrofluoric acid is preferably employed as the chemical solution.
In the methods of treating semiconductor substrates, the concentration of the hydrofluoric acid is preferably controlled to change during the treatment of the semiconductor substrates. Further, the concentration of the hydrofluoric acid and the concentration of the ozone are controlled preferably to change oppositely during treatment of the semiconductor substrates. Still further, the concentration of the hydrofluoric acid and the change of the concentration of the ozone are controlled preferably to change periodically oppositely during the treatment of the semiconductor substrates.
Other and further objects, features and advantages of the invention will appear more fully from the following description.